+1 Nice question. I always wondered that myself, but just assumed it was either because in the beginning The Professor and Mary Ann were considered small parts, and later officially became "main characters", or because the actors got mad about it.
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druciferreOct 16 '13 at 12:07

@druciferre - That was my original theory as well.
–
JoshDMOct 16 '13 at 13:00

1 Answer
1

According to TV Series Finale, there was a stipulation in Tina "Ginger, the movie star" Louise's contract stating that she was to be the last person billed in the opening credits. After Louise's contract was signed, the parts now known as "Mary Ann" and "The Professor" were recast to Dawn Wells and Russell Johnson respectively. This casting change, combined with Tina's contract, required them to be placed in the end credits.

According to this Today Show interview (YouTube, @ 3m 30s) with Dawn Wells and Bob "Gilligan" Denver, Denver explains how his own contract stipulated that he could choose his own billing. Before season two began, he declared to the powers-that-be that unless Wells and Johnson were added to the beginning credits for season two, he would move himself to the end credits. The change was made; either Tina Louise agreed to the credit sequence alteration, or her contract was reworked.

Interestingly, this interview was the first time Wells was made aware that Denver's demands were the reason the theme song was changed.

I also witnessed a second variation of the song, which only took place during re-runs. Some syndicates re-running the show manipulated the second half of the theme song, which ran during the end credits. These broadcasts silenced the audio when the words "each week" were sung, transforming

{...} so join us here each week my friends {...}

into

{...} so join us here {SILENCE FOR TWO BEATS} my friends {...}

I presume this was done since the re-runs were broadcast on more frequent intervals than weekly, and the associated networks questioned the intelligence of the viewership.